Analog Microphone Breadboard Ciruit

The goal of this project is to make a working analog microphone out of a breadboard and cheap equipment. There are improvements to be explored and a world of possibilities!

CMA-4544PF-W Microphone

TLV2462 Op Amp

1/8th In TRS Cable

1/8th In TRS Receptacle

Movo USBC-AC2 3.5mm to USB-C Stereo Audio Adapter (or similar mic input TRS input to USB-C sound card)

Assorted Resistors and Capacitors

Jumper Wires

Breadboard

2.75 V Power Supply

APx515B Series Audio Analyzer

Depending on how much gain you want on your mic, select the appropriate resistors to bias the op amps. Values we chose for a 11 V/V gain for mic level and 28 V/V for line level are in our schematic. With more gain comes more volume but also more noise and chances of clipping. Test different values to see what is best for you.

Select capacitor and resistor values for AC bias. The DC voltage at the beginning of the OpAmps must be small enough that the output DC voltage does not exceed the supply voltage, but large enough that the signal does not fall below ground (for example if your AC signal was 15mV Vpp, but you only had a 5mV DC voltage, this would be bad).

Ensure the frequency response of the AC coupling circuits is suitable for the audio signal. Use the equation 3dB = 1/(2𝛑RC) to calculate the frequency at which half the voltage is lost (these coupling circuits are naturally high pass filters). For an audio signal you would at least want the 3dB frequency to be less than 20 Hz. Make sure you don’t use too big of capacitor and resistor values since too large of a time constant can cause delays in startup time and let low frequencies through that you might want to filter out instead.

Follow the schematic above to create your circuit. Note that the TLV2462 Op Amp IC has two op amps in it.

Solder one jumper wire to the ground pin of the TRS receptacle and one jumper to the signal pin. Keep the ground wire connected to ground. If you want to use mic level, connect the signal jumper to the mic level output. If you want to use line level, connect the signal jumper to the line level output.

Acquire a DC power supply and attach the power rail of the circuit to 2.75V (may be different value for your specific microphone if you got a different one so follow the specification sheet of your microphone) and ground the ground rail of the circuit.

Then determine where to attach the output on your specific circuit. Above shows our setup where the lower right leads are attached to mic level and the upper right leads are attached to line level. Note that measuring both at the same time is likely to cause interference that will affect your measurements.

Then use the APx515B Series Audio Analyzer to take measurements of your circuit. Attach the audio analyzer to the outputs on your circuit and then take sweeps. Do separate tests for line level and mic level. In our setup, our orange wire is line level (x28 amplification) and the yellow one (when the yellow is unattached and the yellow connects to the capacitor) is the mic level (x11 amplification).

To get better results than we did, make sure to place the speaker that the sweeps are coming from, to avoid any reflections when the sound is going to the microphone. Having the reflections causes the data to show things other than the direct noise. Although, gating the impulse response can help solve the room reflections because you can make sure that the timing only picks up the direct sound.

Then set up the earthworks microphone to compare it to your analog microphone breadboard circuit. You can do this by setting up the earthworks microphone and attaching it through ARTecessories Phantom Pro Two Channel Phantom Power Supply and then attaching that to the Audio Analyzer. You can additionally repeat this step with any other microphone you want to compare to your own (ex. miniDSP UMIK-1 Measurement Microphone).

As shown in our setup, have the mic as close to your circuit microphone as possible so that any reflections that your circuit microphone has will also be seen by the earthworks microphone.

Take sweeps of the earthworks mic and then append the data of your mic level, line level and earthworks so that they are all on the same graph. You can then look at many different graphs. Our graphs for THD and RMS. Are shown above!

Now you can plug the TRS plug into your mic to USB-C converter and try out your microphone! Attached are our recordings of mic and line levels. This is without any filtering. Note the 60 Hz hum from the room being super prevalent.

There are plenty of ways to improve this project!

1. Design and order a PCB of this circuit
2. Continuing testing and calibrating the analog microphone circuit against the other higher quality microphones
3. Filter and EQ the mic frequency responses
4. Try out different mics and components